This invention relates generally to a connecting rod used for connecting together reciprocating and rotating members in reciprocating piston machines such as combustion engines and compressors. More specifically, the invention is directed to a connecting rod design which is adapted to have press-fitted within its piston pin MS6 and crankshaft bores either bearings or liners. The design allows the piston pin MS6 and crankshaft portions which form the bores of the connecting rod, to deform radially substantially uniformly during the press-fitting operation such that the liner or bearing press-fitted within the respective bores retain a substantially circular shape. This is due to the creation of equal radial resistive forces upon the liner or bearing.
Connecting rods are designed with a piston pin ring portion and a crankshaft ring portion connected together by a connecting member which is connected to the outer periphery of each ring portion. The piston pin ring portion has a bore for receiving a bearing for rotatably receiving a piston pin, and the crankshaft ring portion has a bore for receiving a liner for rotationally receiving the crankshaft. Each ring portion is thus always reinforced and made stronger at the connecting area by the connecting member.
In the past, when a liner or bearing was press-fitted within a respective bore of the ring portions, the forces created by the tight fit caused non-uniform radial deformation of the respective ring portions. This was caused by the reinforcement of the ring portions by the connecting member at the respective connecting areas of the ring portions. Stated differently, the ring portions were not allowed to deform uniformly upon the press-fitting because the connecting member resisted deformation of the ring portion at the connecting area. Since deformation generally occurred in the direction of least resistance, press-fitting a liner or a bearing within a ring portion bore caused the ring portions to take a generally non-circular shape. This was caused by the ring portion deforming radially more in the area of the ring portion which was not connected to the connecting member. Because of this non-uniform deformation, clearances between the crankshaft or piston pin and the bearings could not be held as close as desired. Accordingly, the life of the bearings and thus the combustion engine or compressor was considerably shortened. Further, the forces transferred between the connecting rod, piston, and the crankshaft were not transferred uniformly upon the full contacting surfaces and hence the life of the liners, bearings, connecting rod, piston rod and crankshaft were substantially limited.
The inside diameter of liners or cups after the press-fitting operation can be machined into a more uniform circular shape. However, this does not solve the problem because the non-uniform radial forces of the ring portions create uneven radial distortion at elevated temperatures. Further, machining each liner or bearing bore requires another step in the manufacturing process which is considerably time consuming and costly. Therefore, the method of machining the inside diameter of the liners or cups after press-fitting is not satisfactory.